CHAPTER 7 SSI INTERFACE
Introduction
This chapter describes the system requirements of the Simple Serial Interface (SSI), which provides a
communications link between Zebra decoders (e.g., scan engines, slot scanners, hand-held scanners,
two-dimensional scanners, hands-free scanners, and RF base stations) and a serial host. It provides the means for
the host to control the decoder or scanner.
Communication
All communication between the scanner and host occurs over the hardware interface lines using the SSI protocol.
Refer to the Simple Serial Interface Programmer’s Guide, p/n 72E-40451-xx, for more information on SSI.
The host and the scanner exchange messages in packets. A packet is a collection of bytes framed by the proper
SSI protocol formatting bytes. The maximum number of bytes per packet that the SSI protocol allows for any
transaction is 257 (255 bytes + 2 byte checksum).
Depending on the configuration, the scanner can send decode data as ASCII data (unpacketed), or as part of a
larger message (packeted).
SSI performs the following functions for the host device:
• Maintains a bi-directional interface with the scanner
• Allows the host to send commands that control the scanner
• Passes data from the scanner to a host device in SSI packet format or straight decode message.
The SSI environment consists of a scanner, a serial cable which attaches to the host device, and if required, a
power supply.
SSI transmits all decode data including special formatting (e.g., AIM ID). Parameter settings can control the format
of the transmitted data.
The scanner can also send parameter information, product identification information, or event codes to the host.
All commands sent between the scanner and host must use the format described in the SSI Message Formats
section. SSI Transactions on page 7-3 describes the required sequence of messages in specific cases.
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